Color television system



Nov. 28,1950 A. N. GOLDSMITH 2,531,508

COLOR TELEVISION SYSTEM Filed July 30, 1946 2 Sheets-Sheet 1 AMPLIFIER LTRANSMITTER BIAS CONTROL AMPLIFIER F 4/ 5/45 M CONTROL AMPLIFIER 1 i J rr FIELD FREQUENCY AMPLIFIER GENERATOR ,45 47 MUN/FIELD r V FREQUENCYAMPUF/ER GENERATOR LINE FREQUENCY AMPLIFIER 4 am-mro/z MULT/ LINEINVENTOR FREQUENCY AMPLIFIER GENERATOR BY ALFRED N. GOLDSMITH ATTORN EYNov. 28, 1950 Filed July 30, 1946 A. N. GOLDSMITH COLOR TELEVISIONSYSTEM 2 Sheets-Sheet 2 INVENTOR ALFRED N. GOLDBMITH BY f ATTORNEYfiatented Nov. 28,

invites stares PATENT other some TELEVISION rant 18 Claims.

This invention relates to television systems and more particularly tothe systematic removal of any residual image or electricalnon-uniformity on the photo-sensitive surface of an iconoscope,orthicon, or an analogous camera tube.

The principle of big t storage employed in the iconoscope involvessetting up a flat plate termed the photo-sensitive mosaic, the surfaceof which is illuminated through a lens by the scene to be transmitted,the image of which is focussed upon the mosaic. The flat surfacecontains a coating of globules oi insulated photo-sensitive material.The photo-sensitivity characteristic is employed to release electronsfrom the surface in the form of an electron image. The electron image isnot utilized directly, but is allowed todissipate itself within thetube, the electrons being col lected by an electrode and removed fromthe tube without further use.

The insulation characteristic of the surfaceis employed to preserve theconfiguration of the charge deficiency on the plate. This conservationof charge continues for as long as is required, and the value of thecharge deficiency at any point on the surface continues. to increase thelonger the light is allowed to fall upon it, though not necessarilyuniformly. Consequently, the light is effectively stored in the form ofstored charges, the distribution of which corresponds to that of thelight in the scene to be transmitted.

When the electron scanning beam passes over a picture element, it makesuse not only of the light which illuminates the element at that instant,but also of the light which has fallen on that element since theprevious passage of the scanning beam.

Each globule in the mosaic surface of the icona much more rapid ratethan that at which it' was charged. The sudden discharge acting throughthe capacitance to the signal coating appears as a current impulse inthe signal circuit connected to the signal coating.

It might be assumed that no charge deficiency would be present on themosaic and no signal would appear if the surface was scanned while 2unilluminated. .It is found, however, that a signal does appear. Thesignal reflects the fact that certain parts of the mosaic have becomecharged at the expense of other parts. The unequal distribution ofcharge is explained by the fact that the scanning beam impinging on theglobules of the mosaic frees secondary electrons from them by force ofimpact. These secondary electrons are in part collected by the nearbycollector-anode which is maintained at a positive potential. However,since the mosaic is insulated, no more electrons can leave the platethan reach it, and in consequence, the secondary electrons not collectedby the collector-anode find themselves attracted back toward the plate.The secondary electrons in falling back on the mosaic do so in a more orless distributed shower which is not uniform, however, owing to localirregularities in the secondary-emission ratio of the surface anddiiferences in the distribution of potential arising from the collectingfield. Consequently, the secondary electron shower deposits itself onthe mosaic in irregular distribution. The scanning beam, in scanningthis irregular distribution of charge, produces a spurious signal thatin turn produces an uneven shading in the reproduced image in thereceiver.

The shading or dark-spot effects described above are deleterious incyclic or sequential multi-color television scanning where a successionof pictures are scanned through their re-. spectively related colorfilters, since they may give rise to false color values in certainportions of the image.

It will also be seen that, due to the storage characteristics of themosaic plate, a moving subject would produce a blurred image if the timeinterval allowed for storage of the globules were not reduced to aminimum. By sweeping the charge from the mosaic during the blankingperiod between successive fields or scannings, the elimination of such aresidual image. can be accomplished to alarge extent.

There is an additional type of residual picture, so to speak, which itis sometimes desired to eliminate. If interlaced scanning is used, andif only anodd-line scanning is carried out, a residual image (which mayendure for quite an appreciable period) exists in the even-line spaceswhich are as yet unscanned. Thestrength of such a residual image is acomplicated function of the type of image tube, the scanning beamcurrent, thebeampotential, the sharpness of focus of the beam undervarious conditions, and the like; It issometimes undesirable that suchan unscanned area shall hold a picture, and ac" cordingly the presentinvention becomes useful in the e.imination of such residual images. Thepresent invention may thus be applied for the elimination of allresidual images between successive scannings.

The primary object of this invention, accordingly, is'to provide animproved television system.

Another object of this invention is to eliminate any electricalnon-uniformity or shading effect on the photo-sensitive surface of aniconoscope or similar tube whereby any prior scanning or variable tubecondition may affect alater scanning, it being applicable to-moriochrorne television, color television, stereoscopic televisionorthe like.

A further object of this invention in'oneof its preferred forms is toconfine the period of residual image elimination to a desired valueandto equalize to a predetermined extent theperiod of illumination andelectron image storage -of all portions of the image.

istill another object of this invention is the elimination of anyresidual image, whether covering the entire mosaic of an iconoscope oronly the odd-line or-even-line positions in an interlaced scanningregime. W e I Other and incidental objects of the-invention will beapparent to those skilled in the art from a reading of thefollowingspecificationand an inspection of the accompanying drawinginwhich Figure 1 illustrates schematically apreferred form of thisinvention;

Figures 2a, 2b, 2c, and 2d show graphically the operation of a preferredform of this invention; and r Y W e Fig-ore 3 shows schematically anarrangement whereby image scanning in color television'is carried out inthe shadow of a 'dark 'spoke in the v rotating filter disk or drum, thisspoke following 'agrelatively narrow color filter section.

In order to present for each successive "scanning an electrically freshanduniform mosaic to the scanning process, the mosaic can be swept cleanelectrically, so to speak, between successive scannings and duringjthevertical re turn period between successive field scannings. During thisreturn period, the electron beam of the'iconoscope, with suitablecharacteristics, must pass over every portion of the mosaic during whatmay be termed the image-release period. The preferred characteristics ofv the scanning during the image-release period inclu'de'the following:

1. The intensity of the scanning beam during the image-release periodshall be best suited to that purpose and, in general, greater than thatused for the normal picture scanning. Such control or increase ofintensity of the beam may be accomplished by a correctly timed changingof the iconoscope gun bias suitably to regulate the beam intensity. I

2. The beam-spot area during the image-release scanning may be alteredto the most suitable value for that purpose which, in general, may begreater than that used for the picture scanning so as to create a moreuniform coverage, even overlap, and averaging effect at the mosaic. Thischange in the beam-spot area may also be accomplished by changingcorrespondingly and at appropriate times, the bias on suitable membersof the electron-gun'assembly.

3, In order that the successive image-release scannings shal1 besubstantially identicalf it is desirable that the frequency-of thevertical and represent typical rays passing through lens I.

horizontal deflections durin the image-release period shall be awhole-number multiple of the corresponding normal picture-scanningdeflection frequency. The vertical scanning frequency during theimage-release period, in an illustrative example described in detailbelow, is eight times the vertical scanning or field frequency duringthe normal picture scanning period. It is preferred, as will be shown,that 1 sawtooth scanning waves shall exist during the image-releaseperiod, which would be the same as the brief falling portion of thenormal sawtooth deflection wave for picture scanning. Alternatively anylarger odd number of half sawtooth waves of the image-release periodfrequency shall exist during that period, which period, as stated,correvertical picture-scanning deflection frequency.

If the two ratios are to be the same, the sawtooth waves for theimage-release scanning and 'for the picture-scanning respectively mustbe homologous and similar (that is, the ratio of the time required forthe rising portion of the sawtooth wave to the time required for thefalling-portion of the sawtooth wave shall be the same in bothinstances). It is preferable that the sawtooth waves shall in fact behomologous for the imagerelease scanning and the normal picture scanningReferring now in detail 'to Figure 1, objective lens I on optical axis 3focuses a light image of external subjects on the mosaic 5 of theiconoscope or other suitable camera tube 1. 9 and H An electrode !3controls the intensity of the electron beam I5 which is used forscanning the mosaic 5. Deflection plates I! and 19 are illustrated aspurely representative and conventional means utilized to control theelectron beam in the desired'scanning sequence. Electrode 21 provides acontrol for the focusing of electron beam I5.

The electrode 23 of the iconoscope Y has its usual function of removingsecondary electrons, as well as an accelerating element. The signalplate 25 is used to withdraw the video signal to the amplifier Z1 andthence to the transmitter 29.

It will be seen that, by using the electron beam as a broom, the mosaic5 may be swept free of charge during the image time or interval of timenormally allotted to the return of the electron beam to the positionfrom which it starts its scanning of the image.

The electron beam i5 may be broadened'during the image release time byapplying a proper bias to the focusing control electrode2 Ffrom thefield frequency generator 3!. A signal can also be derived from fieldfrecuency generator 3! properly to control the intensity of the electronbeam.

It is necessary that amplifier 2'! be'bloclre'd during the image releaseinterval in order that any spurious signal obtained from iconoscope 1during that interval will not be transmitted. This can be accomplishedbyprovidingampliflerf'l wi h asutroilbias d ringtheim ee e aseii ne int yalhe b ck glof mplifi 2 ,.ca also eac m lished by d riv ng a si nal bias'f the field frequency generator 3| such that during the blanking periodor image" release period amplifier 21 is blocked and the iconoscope 1 iseffectively disconnected from the television transmitter29. l p "1 Thetype of biasing required for broadening the beam and blocking amplifier2! must necessarily'be greatervin a negative direction during thefalling period of the sawtooth wave derived from the field frequencygenerator 3|. This can be accomplished by providing the field frequencygenerator 3| with an outputcoil 33., Coil ,33 is coupled to bias controlamplifier 35 through coil 31, which is so polarized that the outputSignal from bias control amplifier 35 is greater in a negative directionduring the falling period of the sawtooth wave generated by fieldfrequency generator 3|;

It -follows that during the image release in-v terval a potential isderived from bias control amplifier 35 and applied to electrode 2| tobroaden the electron beam.

During the same interval, a bias is derived from control amplifier 35and applied to amplifier 2'! to cause it to become inoperative for thatinterval.

During the rising portion of the vertical scan ning wave from thegenerator. 3|, the deflection voltagepasses to theiainplifierlsii andthenceto deflection-plates. l9. During the imagezrelease interval, it isneoessary'to prevent-the signal generated by field frequency generator3| from reaching the deflection plates it, so there is-also derived frombias control amplifier 35 a bias p tentia'l whichwill make amplifierEdinoperativ during the image release time interval.

Coil 4| is also coupled to coil 33 so that th voltage induced therein isopposite in-Lpolarit to thatinduced in coil 37. ii

During the image release time intervaL'a bias is obtained from. biasamplifier 23 and applied to intensity control electrode IE to increasethe intensity of the beam during the image release time interval. 1

A multiple field-frequency generator 25 pro duces a sawtooth wave havinga frequency which is a multiple of that of generator 3|. The izieth odsof producing a multiple frequency are well known in the art andnee'd notbe here described. The output of generator 45 passes to amplifier 4'!and thence to deflection plates |9. However, amplifier 47 is biased fromthe output of bias control amplifier 43 to make it operative only duringthe image release time interval because, during the rising portion ofthe sawtooth vertical scanning wave from generator 35, amplifier -43biases amplifier 4'! to cut-off. However, during the falling portion ofthe vertical scan-f ning wave from generator 3!, amplifier t3 activatesor releases amplifier 31 and thus per mits the application of the outputof the multifield-frequency generator :35 to vertical deflection plates|9.

The-arrangement illustrated thus has forits purpose the application to'vertical deflection plates l of the normal picture scanning wave fromgenerator 3| during the rising portion of that wave but the applicationof the multi-field frequency imagez-releasescanning wave fromgenerato1x45 during the -;period when the normal scanning wave, fromgenerator'tl is falling.

The line-frequency generator 5! produces an output which passes "throughamplifier 53 to the horizontaldefiection plates I! in the usual fashion;during the rising portion of the vertical scanning wave producedbygenerator 3|, as a result ofthe bias obtainable from amplifier andapplied to amplifier 53. However, durin the falling portion of thevertical scanning wave from generatortl, the output of the multi'line-frequency, generato1g55, is passed through amplifier 53, to thehorizontal defiectionplates I! as a result of the bias obtained fromamplifier 43.

V Theoverall system'functions as follows: During the rising portion ofthe normal vertical scanning wave, f rom generator 3|, the beamintensity is normal for image scanningof the selected type, the focus ofthe beam has a sharpness suitedto such normal picture scanning, a normalvertical scanning wave is applied to the vertical deflection control,and a normal scanning wave is applied to the horizontal deflectioncontrol. Thus the-usual picture scanning proceedsnormally in allrespects-during the rising portion of the scannil gwave from generator3|. However; during the falling portion of the scanning wave fromgenerator 3|, the beam intensity is altered to any value suitable forimage release or elimination,

the focusing of the spot on the mosaic is correspondingly modified forthe same purpose, and the vertical and horizontal defiectionsaremultiplied in speedso that, at, least one expedited or speededwupcomplete scanning cycle takes place I during the falling portion of thevertical scanning wavefrom generator 3|. For the purpose of explanation,an example is given of 1 image release scanning cycles-taking placeduring the falling portion of the :vertical scanning wave-a relationshipwhich, in general, appears preferable.

In; Figure 2a there is shown the normal vertical scanning wave such asis produced by generators-3|, 596| is the rising portion referredtotaboverand 6 |.'63 is the falling or image release, interval.

Figure 2b shows the multi-field-frequency sawtooth wave such as may begenerated by 45. It will be noticed. that in this illustration, thisimage-release scanning wave has a frequency ei ht times that of. thenormal scanning frequency shown in Figure 2a and that 1 scanning cyclesE5-6Tcorrespond to thefalling portion 51-433 of the scanning wave ofFigure 2a. In Figure 2b, the scanning wave is homologous and similar tothat in Figure 2a, but this is not a necessary condition. For purposesof illustration, the time occupied by portion 6|-63 is approximately 16%0f the entire length of wave 59-63.

' It is obvious that by changing the ratios of the periods occupied by6|'63 and 59-fi|, respec tively,v and by suitably changing the shape ofwave shown in Figure 2!), any desired quantitative relationships for thescanning and blanking pe-' riods may be closely approximated .orreached.

In Figure 20, there are shown details of the normal or image scanningwave and of the imagerelease wave. The amplitude of the latter can bemade slightly greater than that of'the'former in order that they may addup to the composite scanning wave for finite switching times, and asshown in Figure 2d. It is assumed, however, for the purpose ofexplanation that the electronic switching from the output of generator3| to the output of generator 45 is substantially instantaneous. iFigure 2d shows the significant portion of the composite verticalscanning wave for both'picture scanning and image-release scanning.During the period up to 69, both vertical and horizontal deflection,beam intensity, and focus are normal for picture scanning in theiconoscope. During the period from 69 to H wherein the normal verticalscanning wave 13 would fall, the vertical scanning and the horizontalscanning are both of the multiple frequency suitable for residual-imageelimination. And, as will be noted, a complete scanning cycle for imagerelease, namely 69, 15, TI, TI is included within that period.

. The quantitative relationship between the multiefield-frequency usedduring the image-release period and the normal scanning frequency usedduring the picture-scanning period will now be taken up. It isfirstassumed that sawtooth scanning waves are used both for themulti-fieldfrequency generator and for the field-frequency generatorQandthat these waves are homologous. That is, -the ratio of the timeduringwhich the wave rises to its peak from zero amplitude to the time duringwhich it falls from the peak back to zero amplitude is substantiallyidentical for the two waves. Absolute identity is not necessary, but aclose approximation thereto is desirable. If the ratio of the risingperiod to the falling period in each wave is designated as k, and if themulti-field frequency is 172 times the field frequency, and if there are11 complete multi-fieldfrequency cycles occurring during the time of thefalling portion of the field-frequency wave (together'with and precedingby a single coinp'lete falling portion of the multi-field-frequency wavewithin that same period of the falling portion of the mainfield-frequency wave), then it can -be simply shown that:

k equals (mn-1) /n Thus if one completeimageerelease cycle is to beweed, and if Ic equals 9 (that is, the return period in the mainfield-frequency wave is one-tenth of the total cycle), then m equals 11,and the multi-field-frequency i 11 times that of the field frequency.

Similarly,.if:the return period were 15% of the total period for thefield-frequency wave, and if three complete -image-release cycles (plusa falling portion thereof) are to be used during the falling portion ofthe main field-frequency wave, it is found that m equals 21 for thesmallest integral ratio of the multi-field frequency to the fieldfrequency.

Turning now to Figure 3, there is shown one form of mobile color filterand for purpose of explanation takes the'form of rectangular opaquesections BI and B3 in series with strips 85, 81, and 89 representativeof the color filtering areas, being green, red, and blue, respectively.While such filter assemblies are usually of the rotating disk or drum ormulti-segment type, the mobile filter unit illustrated in Figure3 is alongitudinal strip carrying color filter elements separated by opaquesections. In disk assemblies, the color filters will usually besectorial in their shape, and the intervening paque spaces willsimilarly be sectorial, and are usually referred to as spokes.

The direction of motion of the filter strip is indicated by arrow :95.

The breaks SI and 93 are intended to indicate that the-length of thespoke areas is selected appropriately in consideration of the followingdiscussion and that the drawing is not to scale.

The fa e of a ty ical storage camer tub in x mpl an im e orthi on, hasan ima area 99. The ima e Orthicon is described in 8 detail by R. D/Kelland G. C. Sziklai in an article entitled Image Orthicon Camera in theRCA Review for March 1946, vol. VII, No. 1.

Filter strips 85, 81, and B9, in moving in the direction of the arrow95, move vertically downward across the image area 99.

After the scanning operation of a particular image frame, for example, ablue frame, has been completed at a point corresponding to 69 of Figure2d, it is desirable that light shall not fall upon the camera tube faceuntil after completion of the sweeping of the preceding stored images,as is the case at the time corresponding to 1'! in Figure 2d.

The position of the advancing edge of the red filter section 81 at atime corresponding to 11 of Figure 2d may be approximately as indicatedby a in Figure 3. By the time scanning of the red image begins and at atime corresponding .to H in Figure 2d, the advancing edge of the redcolor section 8'! will have reached position b. Figure 3 is drawn toshow the position of the filter at the time scanning of the red imagebegins and at a time corresponding to 7 I in Figure 2d. The advance edgeof the red section 8'! thereafter progresses downward across the imagearea 99 approximately equally ahead of the scanning line process.Scanning therefore may be made to occur somewhat ahead of the shadow ofthe spoke.

As an alternate procedure, a light transmitting color section of thefilter may be caused to travel across the image area altogether ahead ofthe scanning process, so that the scanning takes place in the shadow ofthe spoke.

The width of the light transmitting color filter sections 85, 81, and 89and their relationship to the scanning process will depend on numerousfactors. Among these are the storage capabilities of the camera tube,the type of scanning, whether it be interlaced scanning or not, thesharpness or size of the scanning spot, the sensitivity of the tube, thebrightness of the image falling on the camera tube, the extent to whichsecondary emission from scanning lines or areas creates electricaluniformity over the entire camera tube sensitive surface, and thepermissible degree of color degradation resulting from minor remainingresidual electrical images on the camera tube sensitive surface.

Having thus described the invention, what is claimed is:

1. In a television system having a camera tube with a photo-sensitivesurface and an electron beam for scanning said surface, a method forremoving electrical non-uniformity from said photo-sensitive surfaceduring the interval between each successive field scanning comprisingthe steps of increasing the intensity of said beam during said interval,broadening said electron beam during said interval, sweeping saidphotosensitive surface with said broadened beam during said interval,and blocking the signal output of said photo-sensitive surface duringsaid interval.

2. In a television system having a camera tube with a photo-sensitivesurface and an electron beam for scanning said surface, a method forremoving electrical non-uniformity from said photo-sensitive surfacebefore each successive scanning comprising the steps of actuating anelectrical circuit during the time interval between successive scanningsto derive from said circuit a signal to increase the intensity of saidelectron beam during said interval, broaden the area of impact of saidelectron beam on said photosensitive surface during said interval, causesaid electron beam to sweep the total area of said photo-sensitivesurface during said interval, and block the signal output of saidphoto-sensitive surface during said interval.

3. In a television system having a camera tube with a photo-sensitivesurface and an electron beam and a deflection signal generator to causesaid electron beam to scan said photo-sensitive surface, a method forremoving electrical nonuniformity from said photo-sensitive surfacebefore each successive field scanning comprising the steps of deriving asignal from said deflection signal generator to actuate an electricalcircuit during the time interval between successive field scannings, andto derive from said circuit a signal to increase the intensity of saidelectron beam during said interval, broaden the area of impact of saidelectron beam on said photo-sensitive surface during said interval,cause said electron beam to sweep the total area of said photo-sensitive surface during said interval, and block the signal output of saidphoto-sensitive surface during said interval.

4. In a television system having a camera tube with a photo-sensitivesurface and an electron beam, a deflection signal generator to causesaid beam to scan said photo-sensitive surface, and an amplifier forsaid camera tube, a method for re moving electrical non-uniformity fromsaid photo-sensitive surface before the time interval between eachsuccessive scanning traverse of the total photo-sensitive surfacedimensions comprising the steps of deriving from said deflection signalgenerator a signal to actuate an electrical circuit during the timeinterval between successive scanning traverse of the totalphoto-sensitive surface dimensions and to derive from said circuit asignal to increase the intensity of said electron beam during saidinterval, broaden the area of said electron beam on said photo-sensitivesurface during said interval, cause said electron beam to sweep thetotal area of said photosensitive surface during said interval, andblock the outputof said amplifier during said interval;

5. In a television system having a camera tube with an image surface andan electron beam, and a deflection signal generator to cause saidelectron beam to scan said image surface, a method for removing anyelectrical non-uniformity from the total image surface before eachsuccessive scanning comprising the steps of deriving from saiddeflection signal generator a signal to actuate an electrical circuitduring the time interval between successive scannings and to derive fromsaid circuit a signal to increase the intensity of said electron beamduring said interval, broaden the area of impact of said electron beamon said image surface during said interval, actuate a second deflectionsignal generator to cause said electron beam to sweep the total area ofsaid image surface during said interval and block the signal output ofsaid image surface during said interval.

6. In a television system having a camera tube with a photosensitivesurface and an electron beam for scanning said surface, a fieldfrequency generator and a line frequency generator to provide deflectionvoltages for said electron beam, a method for removing electricalnon-uniformity from said photo-sensitive surface before each successivescanning comprising the steps of deriving from said field frequencygenerator a signal to actuate an electrical circuit during the timeinterval between successive scannings and to derive from said circuit asignal to increase the intensity of said electron beam during saidinterval, broaden the area of impact of said electron beam on saidphoto-sensitive surface during said interval, actuate a multi-fieldfrequency generator and a multi-line frequency generator to cause saidelectron beam to swee the total area of said photo-sensitive surfaceduring said interval, and block the signal output of saidphoto-sensitive surface during said interval.

7. In a television system having a camera tube with a photo-sensitivesurface and an elzctron beam, a field frequency generator, and a linefrequency generator for causing said beam to scan saidphoto-sensitivesurface, and an amplifier for said camera tube, a methodfor removing electrical non-uniformity from said photo-sensitive surfaceduring the interval between each successive scanning comprising thesteps of deriving from said field frequency generator a signal toincrease the intensity of said electron beam during said interval,broaden the area of impact of said electron beam on said photo-sensitivesurface during said interval, block the signal from said field frequencygenerator, line frequency generator, and amplifier, and activate a fieldfrequency generator and a multi-line frequency generator to cause saidelectron beam to sweep the total area of said hoto-sensitive surfaceduring said interval.

8. In a color television system having a camera tube with aphoto-sensitive surface adapted to receive an image of an object, anelectron beam for scanning said surface and a mobile color filterpositioned adjacent said camera tube and comprising a plurality of colorsections separated by opaque sections, a method for removing electricalnon-uniformity from said photo-sensitive surface during the intervalbetween each successive scanning comprising the steps of increasing theintensity of said beam during said interval, sweeping saidphoto-sensitive surface with said broadened beam during said interval,blocking the signal output of said photo-sensitive surface during saidinterval, and positioning during said interval one of said opaquesections between said photo-sensitive surface and the position of saidobject.

9. In a color television system having a camera tube with aphoto-sensitive surface adapted to receive an image of an object, anelectron beam for scanning said surface and a mobile color filterpositioned adjacent said camera tube and comprising a plurality of colorsections separated by opaque sections, a method for removing electricalnon-uniformity from said photo-sensitive surface during the intervalbetween each successive scanning comprising the steps of increasing theintensity of said beam during said interval, sweeping saidphoto-sensitive surface with said broadened beam during said interval,blocking the signal output of said photo-sensitive surface during saidinterval, and positioning one of said color sections between saidphoto-sensitive surface and the position of said object only during atime period other than during said interval.

i=3. In a color television system having a camera tube withphoto-sensitive surface adapted to receive an image of an object, anelectron beam for scanning said surface and a mobile color filterpositioned adjacent said camera tube and comprising a plurality of colorsections separated by opaque sections, a method for removing electricalnonuniformity from said photo-sensitive surface during the intervalbetween each successive scanning comprising the steps of increasing theintensity of said beam during said interval, sweeping saidphoto-sensitive surface with said broadened beam during said interval,blocking the signal output of said photo-sensitive surface during saidinterval, and positioning one of said color sections between saidphoto-:sensitive surface and the position of said object only during theperiod of the time occupied by said scannings.

11. In a color television system having a camera tube with aphoto-sensitive surface adapted to receive an image of. an object, anelectron beam for scanning said surface and a mobile color filterpositioned adjacent said camera tube and comprising a plurality .ofcolor sections separated by opaque sections, said color sections beingrelatively small with respect to said opaque sections, a method forremoving electrical non-uniformity from said photo-sensitive surfaceduring the interval between each successive scanning comprising thesteps of increasing the intensity of said beam during said interval,broadening said electron beam during said interval, sweeping saidphoto-sensitive surface with said broadened beam during said interval,blocking the signal output of said photo-sensitive surface during saidinterval, and positioning during said interval one of said opaquesections between said photo-sensitive surface and the position of saidobject.

12. In a television system containing a camera tube having a lightsensitive electrode, an electron beam adapted to scan said electrode, anintensity control electrode, a focusing electrode, and deflectionelectrodes for said electron beam, an amplifier for said camera tube, asystem for the removal of an electrical non-uniformit from said lightsensitive electrode prior to each successive field scanning comprisingin combination a circuit actuated during the interval between successivefield sca'nnings and connected to said intensity control electrode toincrease the intensity of said electron beam during said interval, acircuit connected to said focusing electrode to broaden said electronbeam during said interval, a circuit connected to said deflectionelectrodes to cause said broadened electron beam to sweep said lightsensitive electrode, and a circuit connected to said amplifier to blocksaid amplifier during said interval.

13'. In a television system containing a camera tube having an imageelectrode, an electron beam adapted to scan said electrode, an intensitycontrol electrode, a focusing electrode, and deflection means for saidbeam, an amplifier for said camera tube, a field frequency generator anda line frequency generator to roduce deflection signals for saidelectron beam, a system for the removal of any electrical non-uniformityfrom said electrode prior to each total scanning of both dimensions ofsaid electrode comprising in combination a circuit connected to saidfield frequency generator to derive therefrom a signal potential duringthe interval between said successive scannings, a connection betweensaid circuit and said intensity control electrode, focusing electrode,deflection means and said amplifier to increase the intensity of saidelectron-beam, broaden said beam to cause said electron beam to sweepsaid light sensitive electrode during said interval and to block'saidamplifier during said interval.

14. In a television system containing a camera tube having a lightsensitive electrode, an electron beam adapted to scan said electrode, anintensity control electrode, a focusing electrode, and

deflection electrodesfor said beam, an amplifierfor said camera tube, afield frequency generator, and a line frequency generator to producedeflection signals for said electron beam, a system for the removal ofany electrical non-uniformityfrom said light sensitive electrode priorto each scanning comprising in combination a multi-field frequencgenerator, a multi-line frequency generator, means connected to saidfield frequency generator to derive therefrom a signal to increase theintensity of said electron beam, broaden said electron beam and. tocause said multL-field frequency generator and said multi-line frequency generator to produce a deflection signal for said deflectionelectrodes and timed to cause said electron beam to sweep said lightsensitive electrode during the interval between successive scannings.

15. In a color television system containing a camera tube having a lightsensitive electrode, an electron beam adapted to scan said electrode, anintensity control electrode, a focusing electrode, and deflectionelectrodes for said electron beam, a system for the removal of anyelectrical nonuniformity from said light sensitive electrode prior toeach different color scanning comprising in combination a circuitactuated during the interval between successive different colorscannings and connected to said intensity control electrode, focusingelectrode, and deflection electrodes to cause said electron beam tosweep said light sensitive electrode during said time interval betweensuccessive different color scannings, and a mobile color filterpositioned adjacent said camera tube and comprising a plurality of colorsections separated by opaque sections, said color sections beingrelativel small with respect to said opaque sections.

1.6. In a color television system containing a camera tube having alight sensitive electrode,

an electron beam adapted to scan said electrode, an intensity controlelectrode, a focusing electrode, and deflection electrodes for saidelectron beam, a system for the removal of any electrical non-uniformityfrom said light sensitive electrode prior to each scanning comprising incombination a circuit actuated during the interval between successivescannings and connected to said intensity control electrode, focusingelectrode, and deflection electrodes to cause said elecralit-y of colorsections separated by opaque sections, said color sections beingrelatively small with respect to said opaque sections, and said mobilecolor filter adapted to present one of said opaque sections to opticallblock out said electrode during said interval.

17. In a color television system containing a camera tube having a lightsensitive electrode, an electron beam adapted to scan said electrode, anintensity control electrode, a focusing electrode, and deflectionelectrodes for said electron beam, a system for the removal of anyelectrical non-uniformity from; said light sensitive electrode prior toeach scanning comprising in combination a circuit actuated during theinterval between successive scannings and connected to said intensitycontrol electrode, focusing elec trode, and deflection electrodes tocause said, electron beam to sweep-said light sensitive electrode duringsaid time interval between successive scannings, and a, mobile colorfilter posi- 13 tioned adjacent said camera tube and comprising aplurality of color sections separated by opaque sections, said colorsections being relatively small with respect to said opaque sections,said mobile color filter adapted to present one of said color sectionsonly to the optical path of said electrode during said interval.

18. A color television system comprising in combination a cathode rayscanning tube having an output circuit and having a control electrode, m

a source of bias for said control electrode, a cathode ray focussingelectrode for said cathode ray tube, a source of potential for saidfocussing electrode, a signal amplifier connected to said outputcircuit, means for changing the bias on said control electrode in apositive direction, means for changing the potential of said source ofpotential for said focussing electrode, means for blocking thetransmission of signals through said amplifier, and a keying circuitconnected to said bias changing means, said potential changing means andsaid blocking means for causing each of said means to operate onlyduring the time interval between successive field scannings of saidcathode ray tube.

ALFRED N. GOLDSMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,312,792 Bamford Mar. 2, 19432,413,075 Schade Dec. 24, 1946 2,435,963 Goldmark Feb. 17, 1948

